A celebrity in a fandom I'm in once said she got a custom-made pantsuit from a fan that fit perfectly. I wondered for ages how said fan knew her exact size and measurements.

Reportedly, some fans of another celebrity in the same fandom found out where her children went to school and showed up at the school from out of state, posing as parents and peeking in classroom windows to see if her kids were in there. Only I'm pretty sure that they were adults.